Miniature positioning systems are useful for many applications including micro optics, imaging, medical devices, industrial instruments, and consumer electronics. Piezoelectric stick-slip actuators may be utilized to optimize size, power, and precision of the positioning system. An example of a stick-slip stage, operating at audible frequencies, is presented in U.S. Pat. No. 4,195,243 for a piezoelectric wafer mover, which is hereby incorporated by reference herein in its entirety. However, operation at ultrasonic frequencies, in which the operating noise is substantially inaudible, is highly desired for consumer products and medical devices. Examples of ultrasonic stick-slip actuators include: U.S. Pat. No. 5,225,941 for a driving device; U.S. Pat. No. 5,587,846 for a lens moving apparatus; and U.S. Pat. No. 8,059,346 for a linear drive system, each of which are hereby incorporated by reference herein in their entirety.
Commercial examples of ultrasonic stick-slip stages include the “smooth impact drive mechanism” (SIDM) sold by Konica Minolta (Japan) and the “tiny ultrasonic linear actuator” (TULA) sold by Piezoelectric Technologies (Korea). The SIDM is described in “Development of Linear Actuators Using Piezoelectric Element”, Electronics and Communications in Japan, Part 3, Vol. 81, No. 11, 1998).
An ultrasonic stick-slip actuator generally includes a first body that is frictionally coupled to a second stationary body. One of the bodies must generate asymmetric pulses at the friction contact point, with unequal forward and reverse velocities and accelerations. For movement to occur, the slower direction of pulse velocity and acceleration is insufficient to overcome the friction between the two bodies while the faster direction of pulse velocity and acceleration is sufficient to overcome the friction between the two bodies, which creates a small relative movement between the two bodies during each asymmetric pulse cycle. These small movements may be less than one micrometer, but when added together create longer range movement. By switching the direction of the asymmetric pulse, the direction of motion is reversed. The asymmetric pulses can be created using piezoelectric or electrostrictive ceramic actuators that are energized by non-symmetric electrical drive signals. Piezoelectric actuators can be very small and still produce powerful and small amplitude asymmetric pulses that make it possible to produce highly miniaturized motion systems.